First things first, I am not trying to discourage you at all but you are asking for help on this forum and not really providing any clear explanation of the situation (which I know can be difficult when dealing with electrical issues).
Next, the fact that you built the car from a roller is commendable but I don't know what leaving the car outside has to do with any of this as I never said or hinted at anything like this. I get it that you don't want to take the car to anyone and given that you don't have someone locally available is an issue. I wasn't trying to say that you can't do it, I was trying to offer you an option for situation that you seemed to be stuck at. I don't take my cars to anyone else either so I completely get it.
As to me not knowing as much as I think I do, the same can be said about pretty much every human however I have owned well over 100 vehicles (vast majority of them being Mopars), been working on Mopars since 1975, have built a number of cars from the ground up (am building a 69 Ply Wagon for a client now, have a 70 Roadrunner to build for another client wailing which will be a complete build, have my 71 Charger that getting a 5.7/5spd which is a complete build waiting along with my 70 Roadrunner which also another complete build), designed and built my own wiring harnesses, etc. so I am pretty sure I know what I know.
Now with all of that out of the way, perhaps we can attempt to move forward....
From what you have written I understand you have the following problems;
1. the car will not start? Will it turn over?
2. something to do with a A/C relay making the horn go off? From what I can see on the wiring diagram there isn't a AC relay, there is a horn relay and possibly a time delay relay for the headlights (if so optioned). Given that the horn is going off I think we are talking about the horn relay.
Just an FYI, a Chiltons manual is great for many things but not so much when it comes to electrical, you really need the Factory Service Manual which you can get for free from www.mymopar.com
Its unfortunate that this site doesn't take pictures which would be helpful, but it is what it is. If you don't want my help, so be it